Numerous structures already exist for making volume-enclosing constructions such as conservatories by building up a frame of bars. Examples are described in published British patent applications nos. 2 078 274 and 2 093 144. When said structures need to be load-carrying structures, it is common practice to use steel components which are assembled on site by welding. Once the frame has been assembled, bars of light alloy, and in particular of aluminum, are used for making the facings of the volume-enclosing construction, and these bars are subjected only to minimal forces which are extremely small compared to those which the steel frame is required to withstand.
It is tempting to use light alloy bars for making a load-carrying structure when providing a volume-enclosing construction including at least a first plane which is defined by load-carrying bars running parallel to one another, and further including at least one other plane which intersects the first, i.e. which constitutes the geometrical figure of a dihedral. In order to make this possible, it is necessary to solve the problem of transmitting forces between the two planes under consideration of the load-carrying structure.
When the line of intersection between the intersecting planes runs orthogonally to the directions in which the load-carrying bars extend, the problem may be solved by providing a simple direct link between the adjacent ends of the load-carrying bars. Such a solution is illustrated, for example, in U.S. Pat. No. 4,327,532.
However, when the line of intersection between the planes may be at an arbitrary angle relative to the direction of the load-carrying bars defining one, or in particular both, of the intersecting planes, it becomes difficult to design a simple inter-plane link by virtue of the complication inherent to assembling such planes if the resulting assembly is to be rigid enough. Thus, for example, when using a variable angle assembly of the type described in the above-specified U.S. patent, direct fixing to the webs of the bars is not suitable, in particular when forces are to be transmitted. This becomes even more difficult to provide when the line of intersection is no longer orthogonal to the direction along which the load-carrying bars extend. That is why steel bars which are assembled mechanically and by welding are preferred for complicated frames in spite of the difficulties of using special equipment on site, such as welding equipment, and in spite of the resulting frame having poor resistance to corrosion. Furthermore, the need to ensure that such a volume is acceptable in appearance leads to the use of additional facing components, thereby further increasing manufacturing time and also making it difficult to perform periodic inspections of the vulnerable areas of the frame in which weaknesses may be started by fatigue and/or corrosion phenomena.
Preferred embodiments of the present invention provide a load-carrying structure capable of being made from bars of light alloy (and in particular from aluminum bars), using conventional mechanical assembly techniques, and in particular avoiding the need for welding.
An aim of the invention is to provide a load-carrying structure which is particularly suitable for making any shape of roof framework, and is also capable of being placed against facade frameworks or against the main structure of a building, said load-carrying bars being capable of extending over a wide range of directions relative to each other when defining any given pair of intersecting planes.
Another aim of the invention is to provide a load-carrying structure having subassemblies capable of being pre-assembled in a factory, thereby further reducing on-site assembly time.
Another aim of the invention is to make it possible to provide load-carrying frames having a wide variety of prismatic shapes, and in particular to provide all shapes of roof frame, e.g. valleys or gables, etc. In other words, the invention is generally applicable to any type of join between roofing planes, or between facade planes, or between a roofing plane and a facade plane, regardless of whether any of the planes intersecting along a given line are vertical or not.